Fibre-glass moulding process

ABSTRACT

A process for making glass fibre reinforced mouldings, in which the moulding resin is injected into the space between a pair of dies defining between them the shape to be moulded, and in which space is located a glass fibre mat with its edges pinched between the edges of the dies, the opening between the dies at the edges where the mat is so pinched being such as to allow air to escape while providing an impedence to the flow of resin therethrough.

United States Patent 1191 Appl. No.: 138,190

Foreign Application Priority Data Apr. 29, 1970 Great Britain 20,638/70References Cited UNITED STATES PATENTS 9/1959 Jonke 264/258 NewloveSept. 25, 1973 FIBRE-GLASS MOULDING PROCESS 2,847,712 8/1958 Pollard264/328 x 2,962,764 12/1960 Trojanowski 264/316 [76] invemor- 2,495,6401/1950 Muskat 2154/010. 53

Norfolk, England [22] Filed: Apr. 28, 1971 Primary Examiner-Donald J.Arnold Assistant ExaminerRichard R. Kucia Attorney-Molinare, Allegretti,Newitt & Witchoff [5 7] ABSTRACT 6 Claims, 6 Drawing FiguresPATENTEDSEPZSLBH SHEET 2 BF 2 1 AN A/E mum/.5

Inventor FIBRE-GLASS MOULDING PROCESS This invention relates to aprocess for glass fibre reinforced mouldings and to mouldings madethereform.

The most common glass fibre moulding process comprises a so-called handlaying up method wherein a mat of glass fibre is laid over a shaped dieand the resin for binding the fibres is worked into the fibres of themat by brushing or rolling. Such a process is time consuming andrequires skilled labour. Another method of moulding more recentlydeveloped is the so-called cold press moulding, wherein a mat of glassfibre, usually of long fibres, together with a resin are compressedbetween two heavy dies. The dies have to be forced together at a slowrate in order to ensure that the resin penetrates through the mat. Adraw-back in such a process however is that there is a likelihood of airbeing trapped between the dies with a consequent blemish or pocket beingformed in the required moulding. Further the apparatus by its verynature is heavy, cumbersome, complicated, expensive and in any case theequipment involved is tied up for a considerable time while the resinsare curing.

The present invention aims to overcome the drawbacks of processes usedhitherto by providing a process which is less time consuming, requiresless complicated and expensive apparatus and is more effective inpreventing blemishes.

To this end according to the invention the moulding resin is injectedinto the space between a pair of dies defining between them the shape tobe moulded, in which space is located a glass fibre mat with its edgespinched between the edges of the dies, the opening between the dies atthe edges where the mat is so pinched being such as to allow air toescape while providing an impedance to the flow of resin therethrough.

It is not possible to be too specific in connection with the die spacingat the pinch-off but it is believed that it is important to control theair flow therethrough in addition impeding the resin flow. As apractical matter I have found that a pinch-off of 0.005-0.007 ins. perounce weight/sq.ft. of glass fibre reinforcement employed in the mouldleads to the production of a successful moulding.

Preferably the glass fibres of the mat are of the long continuous typealthough it is believed that the process can be applied with the shortglass fibres which are quite commonly employed in the glass fibremoulding industry or with other forms of glass fibre such as theconventional needle-mat. What is important is that the mould cavity issubstantially filled with glass fibre.

Because the injection pressure can be relatively small (i.e., generallyaround 50 lbs./sq.ins) the dies can be of a relatively lightconstruction provided of course that they are sufficiently rigid toavoid distortion and thus the heavy cost of the dies and equipmentassociated with cold pressure moulding is avoided. In practice of theinvention, dies of glass fibre moulded materials have been foundconvenient.

The process of the invention lends itself readily to mass productionmethods. Thus, for example, a series of dies can be set up and theinjection equipment moved from die to die, injection being carried outat dies along the line while curing is taking place in dies which havebeen previously injected.

A very important consequence of the invention is the considerable timesaving which is achieved over hand laying-up and cold pressure moulding.We have found from experience in moulding one particular article thatwhereas the pressing in the cold pressure moulding technique took of theorder of 20 minutes the moulding by the injection method of theinvention took of the order of 2 to 3 minutes. Another example is amoulding which was formerly hand laminatted and taking lhr 10 minutesbeing injected in l 1 see.

As to the nature of the resins employed it is believed that thepolyester resins which are commonly employed in glass fibre mouldingtechniques are very suitable in the process of the invention.

The invention will be further described by way of example with referenceto the accompanying drawings in which:

FIGS. 1 is a perspective view of a pair of dies which may be used incarrying out the present invention;

FIG. 2 is a section through the two dies taken at the edge;

FIG. 3 is a diagram of a typical apparatus for injecting the resin;

FIG. 4 is a cross-section of a practical embodiment of mould arrangementfor use in the present invention;

FIG. 5 is an enlargement of a part of the arrangement shown in FIG'. 4;and

FIG. 6 is an alternative to the arrangement shown in FIG. 6.

Referring to the drawings, in FIG. 1 is shown in perspective a pair ofdies suitable for moulding for example a feeding trough. The dies 2 and4 are complementary and define between them the shape to be moulded(i.e., the moulding cavity). In practice the two dies will be clampedtogether so as to leave a pinch-off space 6 through which air can escapewhen the resin is fed in to the die space through the inlet or injectionsocket 8. When assembled as shown in FIG. 1 the fibre mat will bearranged inside the moulding cavity and will project to the edges andinto the pinch-off 6 and as will be seen from FIG. 2 thefibres arepressed together at the pinch-off 6.

Referring again to FIG- 2 the outer periphery 10 of the mould 2 isbrought closer to the surface of the die 4 so as to squeeze the fibresbut not sufficiently to prevent air escaping through the pinch-off 6.The closing up of the two dies together with the fibres trapped in thenarrow opening forms an impedence preventing the waste or resin afterinjection has ceased. In practice the operator injects the resin intothe opening 8 and observes when the resin starts to escape through theopening 6. When the resin appears to have filled the whole of theopening, injection is terminated whereupon further escape is preventedby the impedence.

The apparatus as shown in FIG. 3 comprises conventional charging tanks12 and 14 which are pressurized through air pressure lines 16 wherebythe surface of the resin in the inner containers 118 is depressed so asto force resin through 'the lines 20. The lines 20 converge on amechanical mixer 22 driven by an air motor 24. The mixer being a purelymechanical device and merely driven by an air motor effects the mixingwithout introducing air into the resin so that the mixed resin fed fromthe mixer issues through lines 26 free of air. The line 26 is, when theapparatus is in use, plugged into the feeder 8 of the upper die.

As an alternative to the pressurised tanks pumps may be employed fordelivering the resins to the mixer 22, an arrangement comprising twopumps, one for each of the substances to be mixed, obviously being themost suitable.

The nozzle 26 has a morse tapered end for plugging into a complementarymorse tapered feeder 8. in general a morse tapered plug is inserted intothe feeder 8 after injection.

The pressures required for delivering resin to the mixer will, ofcourse, vary according to the circumstances but in practice we havefound that pressures up to 100 lbs. and more generally about 50 lbs. persquare inch are adequate for most pusposes.

The whole of the apparatus shown in FIG. 3 can be mounted on a trolleyor carriage capable of being easily moved from mould to mould. Thus theapparatus and method of invention are very suitable for line production.

The resins employed in the two tanks are usually thermosetting polyesterresins and as is common practice one container will incorporate anaccelerator and the other container will contain a catalyst.

In the arrangement shown in FIG. 4 glass fibre reinforced polyester dies2 and 4 (which are shown in section) are held in relative positions insteel frames 30,32 which give rigidity to the dies. The frames 30,32 areclamped together during injection and precise relative location of thedies is provided by location dowells 34 on frame 30 which engage insockets 35. The injection socket 8 is normally centrally situated, thisbeing found to allow greater tolerance at the pinch-off.

The arrangement of FIG. 4 is suitable for mouldings which finish on avertical edge in which case it is convenient to have the pinch-off 8extending as shown at 45 to the vertical.

It is an advantage to fit two or three 0.005 inch steel shims underlocation dowells 34 to provide a degree of adjustment to the pinch-off.

The alternative structure of FIG. 6 is suitable in the case where themouldings finish on a horizontal flange.

One cannot be too specific as to the viscosity of the resin to beemployed. in fact it is believed that the process of the invention isoperable over a very wide viscosity range provided that there is a largedifference between the viscosity of the resin and the air to beexpelled. As a practical matter it has been found that the commerciallyavailable polyester resins do have a suitable viscosity for carrying outthe process.

I claim: 1. A process for molding parts from liquid resin reinforcedwith glass fibers which comprises:

providing a mold having a pair of dies, said pair of dies definingbetween them a cavity corresponding to the shape of said part to bemolded and having cooperating spaced flanges around their peripherres;placing glass fibers having marginal edges within said cavity, saidmarginal edges extending between said flanges; compressing said marginaledges of said glass fibers between said flanges to a predeterminedthickness such that said glass fibers permit the escape of air from saidcavity and impede the escape of said liquid resin from said cavity;

injecting into said cavity under relatively low positivesuperatmospheric pressure said liquid resin containing a curing agent;de-aerating said cavity through said marginal edges of said glass fibersduring said injecting step;

continuing said injecting and de-aerating steps at least until saidliquid resin begins to escape through said marginal edges;

reducing the pressure on said liquid resin to approximately atmospheric;

curing said liquid resin to a hard, rigid state;

and removing said molded part from the mold.

2. The process claimed in claim 1 wherein said compressing step includesinserting shims between said pair of dies and clamping said pair of diestogether, said shims maintaining said predetermined thickness.

3. The process claimed in claim 1 wherein said predetermined thicknessis 0.005 to 0.007 inches per ounce per square foot of said glass fibersused in said process.

4. The process of claim 1 wherein said positive superatmosphericpressure is less than pounds per square inch.

5. The process of claim 1 wherein said liquid resin is a thermosettingpolyester resin.

6. The process of claim 1 wherein said glass fibers substantially fillsaid cavity.

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2. The process claimed in claim 1 wherein said compressing step includesinserting shims between said pair of dies and clamping said pair of diestogether, said shims maintaining said predetermined thickness.
 3. Theprocess claimed in claim 1 wherein said predetermined thickness is 0.005to 0.007 inches per ounce per square foot of said glass fibers used insaid process.
 4. The process of claim 1 wherein said positivesuperatmospheric pressure is less than 100 pounds per square inch. 5.The process of claim 1 wherein said liquid resin is a thermosettingpolyester resin.
 6. The process of claim 1 wherein said glAss fiberssubstantially fill said cavity.